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LED Resistor Calculator
You have to know three things o calculate the resistor:
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Supply voltage This is how much power you're putting into the circuit. Batteries and wall warts will have the output voltage printed on them somewhere. If you're using multiple batteries*, add the voltage together.
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LED Voltage Sometimes "Forward Voltage" but usually just abbreviated "V".
Led Forward Voltage:Amount of voltage that the led requires to light up properly.
If you don't know the exact voltage rating of the led, you may use the following values as a guide. Note! They may not be the exact values for your leds. Lower voltage is always safer!
Standard Red: 1.7
Super Bright Red: 2.2
Standard Green: 2.2
High Intensity Blue: 3.0 - 3.5
High Intensity White: 3.0 - 3.5
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LED Current Sometimes "Forward Current". This is listed in milliamps or "mA".
Amout of current that the led uses when powered up properly. 3 mm and 5 mm leds usually operate in the range of 20 - 30 mA. 20 mA is usually a good value to try here. Lumileds and other super bright units can have requirements >200 mA.
| Singe LED |
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| LEDs in series |
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| LEDs in parallell |
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ref:
http://www.instructables.com/id/Choosing-The-Resistor-To-Use-With-LEDs/
http://ledz.com/?p=zz.led.resistor.calculator#series
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